Depth sensing technology can be used to determine a person's location in relation to nearby objects or to generate an image of a person's immediate environment in three dimensions (3D). An example of depth sensing technology is a time-of-flight (ToF) depth camera. A ToF camera has a light source to emit light onto nearby objects. Light reflected off surfaces of the objects can be captured by the ToF camera. The time it takes for the light to travel from the light source of the ToF camera and reflect back from an object is converted into a depth measurement (i.e., distance to the object), which can be processed to map physical surfaces in the user's environment and, if desired, to render a 3D image of the user's environment. Another example of depth sensing technology is based on phase delay calculations. Emitting light at one or more known frequencies and comparing the phase of received reflected light with that of the emitted light enables a calculated phase delay. Knowing one or more phase delays of the reflected light enables a processor to determine the distance to the object from which the light was reflected.
Illumination systems draw power to operate. In mobile devices, there are often strict constraints on power consumption, as well as size, weight and cost. The greater the illumination power of a light source is, the greater is the power draw. This issue is present in a number of devices such as depth sensing, active infrared (IR) modules, night vision cameras, security cameras, and other applications of machine vision. The active illumination power of these systems is typically chosen to meet the worst expected operating scenario for the system. Setting the illumination power for the worst case results in over-illumination in many cases, thereby wasting power. Further, a device designed to provide active illumination for the worst case tends to require a power source (e.g., one or more batteries) with more capacity, and therefore more size and weight, than would otherwise be required, thereby undesirably adding to the size, weight and cost of the end product.